1. Field of the Invention
This invention relates to the field of solid state electronics and particularly to the field of microwave amplifiers.
2. Description of the Prior Art
Hybrid microwave amplifiers using field effect transistors (FETs) are well known in the art. The performance of these hybrid amplifiers can be substantially increased by the monolithic integration of the FETs and the passive circuit components. Undesirable parasitic elements associated with packaged devices can be eliminated and improvements achieved in bandwidth, gain, and noise figure. Monolithic integration also eliminates wire bonds between circuit components and the necessity for fine-tuning of the circuit to obtain the desired performance. In addition, a large number of circuits can be processed in parallel.
Attempts to provide a completely monolithic microwave amplifier have encountered difficult problems. It is desirable to provide a circuit having a broadband impedance match at the input and output of the amplifier. The use of passive circuit elements to solve this problem is difficult and requires the expenditure of precious chip area. When the dimensions of microstrip and coplanar transmission lines are reduced in order to conserve space, insertion losses are increased considerably. Additionally, the construction of high Q lumped inductors is a difficult task because of the necessity of accounting for stray capacitance.
In prior art microwave amplifiers (FIG. 1), the source of the FET 1 is connected in common to both the input and output ports 2, 3 of the amplifier, an arrangement referred to as a common source connected FET. The S-parameters for the common source connected FET are shown in FIG. 2 which is a Smith chart (referred to 50 ohms) for a GaAs FET with a gate that is 1 .mu.m long and 300 .mu.m wide. It is noteworthy that the S.sub.11 and S.sub.22 parameters are generally in the high Q regions (particularly for the lower frequencies), thus making it very difficult to match them to 50 ohms over a broadband width.